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Results for “Vinyl Compounds”

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At least 217 records · Page 12Linked to original sources
PubMed2005

Structure, bonding, and solvation of lithium vinylcarbenoids.

[reaction: see text] Molecular modeling was used to determine the structure of lithium vinylcarbenoids in the gas phase and in THF solution. Solvent effects were modeled by microsolvation with explicit THF ligands on each of the lithium atoms. The carbenoid geometries are dependent on the heteroatom and on solvation. The calculations predict 1-chlorovinyllithium and 1-bromovinyllithium to be a mixture of monomer and dimer at 200 K and mostly monomer at higher temperatures, whereas the 1-fluoro-, 1-methoxy-, and 1-dimethylaminovinyllithium are predicted to be dimeric in solution.

Lithium↗
PubMed2005

Catalytic asymmetric diazoacetate cyclopropanation of 1-tosyl-3-vinylindoles. A route to conformationally restricted homotryptamines.

[reaction: see text] Substituted 1-tosyl-3-vinylindoles undergo catalytic asymmetric cyclopropanation with ethyl- and tert-butyldiazoacetate to afford N-protected trans-2-(indol-3-yl)-1-cyclopropanecarboxylic esters in good yield and high enantiomeric excess (81-88% ee). The resulting cycloadducts are demonstrated to be useful intermediates for the synthesis of conformationally restricted, homotryptamine-like analogues such as BMS-505130.

Acetates↗
PubMed2005

Allylstannanes and vinylstannanes from stannylcupration of C-C multiple bonds. Recent advances and applications in organic synthesis.

The stannylcupration of allenes and alkynes has emerged as a powerful tool for the synthesis of allyl- and vinylorganostannanes. The regio- and stereoselectivity of this reaction depends upon the nature of the cuprate, the temperature and the structure of the allene or alkyne. The versatility and synthetic scope of the tin-synthons thus obtained is very wide. These intermediates have been employed as precursors in the key step of the stereoselective synthesis of many natural products, heterocycles or conjugated polyenes. This tutorial review shows a general survey of the recent advances in this area together with the contribution of our lab to this field.

Alkadienes↗
PubMed1991

Effect of column and mobile phase modifications on retention behavior in size exclusion chromatography of polycyclic aromatic hydrocarbons on poly(divinylbenzene).

Results are reported from a study, the goal of which was the reduction of the nonsize effects that govern the size exclusion chromatography (SEC) of planar polycyclic aromatic hydrocarbons (PAHs) on poly(divinylbenzene) (PDVB). Thought to arise from electron-pair donor--electron-pair acceptor (EPD-EPA) interactions between column packing and PAH eluate, nonsize effects could be substantially reduced by the addition of bulky substituents to the PAH, thereby perturbing EPD-EPA interactions between column and eluate. In this work we study the effect of adding a bulky substituent to the column material itself and have selected a sulfonated column material for this purpose. The-SO2OH group provides considerable steric shielding of the PDVB phenyl groups from the PAH eluates and thus its presence could weaken column-eluate interactions, but it is also electron-withdrawing and could possibly aggravate nonsize behavior, because the electron-pair acceptor strength of PDVB could be increased by electron-withdrawing substituents. It was found that either an increase or decrease of EPD-EPA bonding could result with the sulfonated PDVB (S-PDVB) columns, depending on the nature of the mobile phase. Size-dependent elution of PAHs could be obtained with S-PDVB for two classes of PAH by the inclusion of a small amount of hydrogen-bonding solvent, i.e. methanol, to the mobile phase. It is thought that the methanol additive, by strongly hydrogen bonding with the S-PDVB sulfonic acid groups, provides the additional steric shielding necessary to minimize EPD-EPA interactions.

Chromatography, Gel↗
PubMed1975

[Research in antitumoral chemotherapy. X. Cytotoxic and antitumoral activity of beta-nitrostyrenes and of composed nitrovinyl derivatives].

In previous work the antitumoral cytotoxicity of beta-nitrostyrenes obtained by simplification of the aristolochic acid molecule was demonstrated. The effect of modifying the three characteristic parts of the beta-nitrostyrene molecule has now been investigated. The results obtained in vitro and in vivo allow hypothesis of a mechanism of action for the various beta-nitrostyrene and nitrovinyl compounds studied and definition of the maximum simplification compatible with retention of biological activity.

Animals↗